This project is designed to assess the incidence and etiology of post-transfusion hepatitis in newborn infants. Infants transfused during the newborn period and non-transfused control infants are followed for six months after entry into the study. Monthly blood specimens are tested for alanine aminotransferase level and appropriate sera are tested for serologic markers of hepatitis A, B, cytomegalovirus (CMV) and Epstein-Barr virus (EBV). Thus far eight of 160 transfused infants (5.0%) and none of 29 controls who have completed six months follow-up have developed hepatitis. All cases were asymptomatic and there was no serologic evidence of HAV, HBV, or CMV infection (EBV serology is not yet complete).